Worth noting that the artist's impression is... not accurate. Both CD-35 2722 b (the brown dwarf orbiting the primary star) and CD-35 2722 b I (the exomoon orbiting the secondary) should be much closer in size. It is estimated that Jupiter is essentially the largest any gas giant can get; adding more mass will simply increase density and interior temperature until deuterium and lithium fusion and brown dwarfdom, and then at around 80 Jupiter masses, protium fusion and stardom.
Look at Barnard's Star[1], which is actually a fusing red dwarf star: it is not much bigger than Jupiter.
One thing this implies is that the escape velocity of such objects increases linearly with mass, so the surface temperature they can sustain without losing mass increases quadratically with their mass. Massive super-jovian planets can orbit close to their star, limited only by tidal disruption. Some could even orbit within the outer envelope of the star for quite some time.
I kind of assumed the artist’s impression was working with perspective? The images shown in the sidebar seem to picture them at different relative sizes.
If a brown dwarf is right on the edge of stardom would it start protium fusion in only the part of itself that is the right pressure and then slowly burn out or would that ignition precipitate a pressure wave through the entire body forcing fusion to begin everywhere?
The other reply gave good info, but didn't quite answer this. Once an object's core acquires enough temperature/pressure/density to start protium fusion, it will continue, not burn out. The fusion itself increases the temperature, and the produced helium is denser than hydrogen, so the core compresses more under gravity thus increasing the pressure too. So protium fusion creates its own conditions to continue, so there's no such thing as borderline stardom; once protium fusion starts at all, it will continue and it's now a red dwarf. Fusion doesn't begin or occur everywhere, it's still only at the core, but convection will eventually (10^12 year timescale) cause all the hydrogen to have moved through the fusing region.
Thanks; this is much more concise than I could manage.
I think the key idea is fixed minimum/maximum boundaries for a lot of astrophysical phenomena—stellar protium fusion, the Chandrasekhar limit, Tolman–Oppenheimer–Volkoff limit, etc.
I appreciated both yours and the parent's comment. I read the shorter answer first, which was accessible enough to a layman like me that I was left wanting more, which made reading your comment immediately after all the more satisfying.
It should have been obvious to me (fusion duh!) that the result of the fusion is a higher density material that then increases the conditions for the reaction to take place. Both comments were immensely helpful and interesting! Thank you.
There's really a lot to unpack here. (I rewrote this response thrice...) To spoil the answers straight away, and perhaps to address some misconceptions upfront:
> If a brown dwarf is right on the edge of stardom would it start protium fusion in only the part of itself that is the right pressure
The nuclear cross-section of protium fusion in astronomical bodies is determined by temperature, pressure, and density. These variables are in turn dictated by the total mass of the object in question. Brown dwarfs never have sufficient mass for protium fusion, so they never undergo any protium fusion whatsoever. This is a hard-and-fast boundary for stardom.
> or would that ignition precipitate a pressure wave through the entire body forcing fusion to begin everywhere
The three variables above are not uniformly distributed throughout the body; there is a maximum at the centre, and fusion only happens here. Even in the Sun, about 99% of the fusion happens within about a quarter of the radius from the centre. The temperature drops rapidly thereafter, reducing the nuclear cross-section of the proton-proton chain to essentially zero. At the photosphere (surface), the temperature is ~5777 K, which is a decidedly Earthly temperature (lightning bolts are ~ 30000 K). So no, fusion does not happen everywhere.
Now, we need to discuss star formation and why brown dwarfs have never experienced protium fusion at any time in their lives. Star formation is still a very active area of research, debate, and fitting models to empirical study, and this is especially true for the detailed interior and structure of protostars and pre-main-sequence stars; hence, this is going to be quite surface-level (pun not intended).
Collapsing molecular clouds form stars. The total mass of a given cloud (or a particular region of it) sets an upper bound on the resultant object, because the total mass dictates the gravitational potential energy and hence the terminal velocity of the matter, and hence the rate of matter infall at the centre before the cloud dissipates. If the mass is low enough, the central object will become a brown dwarf, or even a large gas giant and a 'rogue planet'.
As the gas cloud collapses, the central region increases in density, temperature, and pressure, but no fusion occurs yet. Conservation of angular momentum forms a circumstellar disc, and material continues to fall onto the central region. As long as this infall continues, the central region is called a protostar. At some point the mass of protostar crosses the boundary needed for deuterium fusion; if the infall stops here, the result is a brown dwarf. If this infall continues, the mass increases beyond the boundary (~80 Jupiter masses) needed for protium fusion, and protium fusion can begin. When the infall stops and the circumstellar disc largely dissipates, the result is a pre-main-sequence star.
Note that both these very young pre-stellar objects are not yet at hydrostatic equilibrium, and are still comparatively rarefied (or 'puffy') compared to main-sequence stars; they are still collapsing, and the temperature, density, and pressure at their cores continues to increase. Only when this equilibrium is achieved and gravitational collapse is halted do stars begin life on the main sequence.
Now, it should be evident why brown dwarfs never experience protium fusion: at no point in their lives have they ever had any region in their interior hot, dense, or hyperbaric enough to have a high enough nuclear cross-section for protium fusion. At their formations, they were simply not massive enough; they continue to collapse, which admittedly provides a considerable power output—surface temperatures are ~1000 K. The largest brown dwarfs experience deuterium/tritium/lithium fusion into helium, but this also stops over time.
(Side note: in my opinion the word 'brown dwarf' is a bit of a misnomer, because look at how bright molten iron (~ 1500 K) is even in broad daylight[1]; now imagine an object ten to twenty times the radius of Earth, emitting this much heat from every square millimetre. If you approached a 'new' brown dwarf it would cast a lot of light.)
Yes; I was under the impression that from context it was clear what I was talking about. In astrophysics, to avoid precisely this confusion, the convention is to use the adjective 'massive' when comparing, well, masses, and 'largest'/'smallest' for the dimension of length and its higher powers (radius/diameter/area/volume). For instance:
Correct, but the link for "super jupiter" also goes to something that astronomers are fairly sure is 1.38x the diameter of Jupiter. Much less massive of course. Meaning Jupiter's diameter is not an absolute hard limit nothing can be larger than.
A small dense planet, which orbits a star, is orbited by a larger gaseous moon. It's interesting the discovery is in Chile which has some of the best night skies, a Class 1 on the Bortle scale specifically in the Atacama Desert. Hoping to make it out there one day.
I recommend it. I'd been living in places that were a class 9 on the bortle scale, with occasional camping trips to places that were a class 5. I recently moved to the south island of New Zealand, and it's a class 4 in town and a class 1 on camping trips nearby. Completely different skies. It's rainy here though, so we don't get cloudless skies nearly as often as Chile does.
At some point I did some research and the Atacama was suggested to me as the best vantage point on earth for simple skygazing. Definitely on my bucket list.
Simple stargazing seems to be selling it short. It's the best seeing on the planet. I can do simple skygazing from my backyard. With a four hour drive I can get to a spot for pretty advanced skygazing. The ESO is building the largest telescope man has ever created in a spot you describe as good for "simple skygazing".
The skies are so dark and clear that some of the indigenous people had "constellations" made up of the dark patches in the sky instead of connecting stars.
I guess it is more of a derivative of the question: "in which bucket should we put the brown dwarf? Is it a star or a planet?".
The answer is neither of course; but since it is more closely related to stars than to planets, I'm more inclined to call this satellite an exoplanet (instead of exomoon).
That being said it is still a nice finding, way more difficult to discover than "normal" exopanets.
'Planet' comes from the Greek word for 'wanderer' which was very useful for labeling the handful of bright stars that moved through the heavens in a pattern. Then we got to the Space Age and kept calling them (and similar new additions) 'planets' even as we learned far more about them. And immediately there's a problem. Setting aside Pluto (and the Sun), you've still got Mercury on one end (5% of Earth's mass, and smaller than several moons) and Jupiter on the other end (320% of Earth's mass - more than everything else in the solar system put together, and over 1000 times Earth's volume). "Planet" stops being a word you can use with any sort of detail. (Thus the IAU definition battle and Pluto's "demotion".) Astronomers have pretty good terminology for stars, but once you go sub-stellar, the labeling rapidly gets difficult, and for good reason.
> Astronomers have pretty good terminology for stars,
...do they though?
The "proper" terminology says all main sequence stars are dwarves, but nobody calls them all that in practice.
Some astronomers insist on saying "yellow dwarf", but some don't really bother.
In general having the only two kinds of star be "giant" or "dwarf" is contentious, but it's also contentious that there isn't a name for whatever is in the "middle". "Main-sequence star" is a broader category and doesn't apply. They're all "stars", obviously, so that isn't specific enough.
The only decent terminology is for the spectral classes, but those only work as long as you look at spectra. The moment you try to figure out what the theory says those stars would look like as proper 3D objects, things get very messy. You also immediately get the issue that star size and brightness goes O>B>A>F>G>K>M. So... it's alphabetic except it isn't. And C is something completely different and doesn't fit the brightness classification at all.
I believe such organisations tend to do such things very intentionally :-)
About ESO [1]
> We are an intergovernmental organisation established in 1962 supported by 16 Member States (Austria, Belgium, Czechia, Denmark, Finland, France, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), our host country Chile and strategic partners.
So Chile has a distinct status, hence the margin...?
More than a special status as a host country, as far as I understand it is explicitly not a member state, hence it's separated from the rest of the flags (Which is curious because despite being the host country, it doesn't guarantee you being a member state of ESO).
The flags have also all (except for Finland, which appears slightly wider?) been squeezed into a uniform 3:2 aspect ratio; some of them (e.g. Belgium, Switzerland, United Kingdom) properly ought to have different proportions. I understand they can look more aesthetically pleasing when they’re all the same size, but it’s another little detail to notice. :-)
An important phrase from the article to consider before commenting: "This system is somewhat hard to define using Solar-System-based words like ‘planet’ and ‘moon’"
The idea of a black dwarf is also pretty wild. The universe isn't old enough for any black dwarves to exist yet, but eventually the brown ones will radiate enough heat away that they're no longer held up by the vibrational energy of the atoms they contain. They'll stop being fluffy and settle into a mode where they're held up only by electron degeneracy pressure (a.k.a the Pauli exclusion principle)... it's a bit like how neutron stars are stable because they're not so massive that they collapse to a black hole. Black dwarves will be stable because they're not so massive that they collapse to a neutron star.
What will this substance look like? Will it ring like a bell if struck? What color will it be? Will it conduct electricity? If so, how? Are the atomic nuclei now the charge carriers because the electrons are stuck? It would likely be a super-thermal-conductor, does that have any analogous properties to a super-electrical-conductor? Which of these can we observe without the sensor collapsing to degenerate matter itself?
I hope there's life around to conduct these experiments when they become possible.
Neutron stars are held up by neutron degeneracy pressure, btw, not electron degeneracy pressure. White dwarfs stars are held up by that (even though they can be very hot; the temperature needed to "lift" degeneracy increases with the mass of the object.) Even the cores of some very large stars are electron degenerate; this is why they remain stable against the "pair production instability": there aren't any states into which newly created electrons can go, suppressing pair production.
I wonder if this thing in turn has something in orbit around it? At the size I wouldn't surprise me if it had satellites of its own in orbit, leaving open the question of what to call them. (I'm no astrophysicist, is this really possible I don't know, but it wouldn't surprise me. What would surprise me is if we could detect them)
“A subsatellite, also known as a submoon, moonlet or informally a moonmoon, is a "moon of a moon" or a hypothetical natural satellite that orbits the moon of a planet”
It might be helpful to describe gravitational relationships with human generational terms of parent-child, grandparent-grandchild, sibling, cousin, etc. So the Sun is the Moon's gravitational grandparent and Jupyter is its parent-sibling (Aunt/Uncle, maybe pibling upwards and nibling downwards).
It is from the Moon's perspective. On the visual spectrum the Earth is much larger and more reflective than the Moon. You're looking at something like 40x greater illumination during a 'full Earth' than you get during a full Moon on Earth. Earth is also extremely noisy in the radio spectrum for radio telescopes, while the Moon itself blocks most of all of that out on the far side.
Earthshine is brighter than moonshine, sure. Earthshine at its brightest, delivers about 0.15W/sq meter to the moon. Sunshine meanwhile delivers 1360W/sq meter to the moon. The near side of the moon is the only side which experiences eclipses. The amount of energy from the sun is SO large, compared to earthshine, that ~1.5 eclipses per year for a few hours each represents a loss of light that outweighs the additional light gained from earthshine by about 5x.
We're talking fractions of a percent here of course, but it's not ambiguous. The near side of the moon is also the darker side.
Details for why ~40x: The Earth is 3.67 times larger in diameter in the lunar sky than the Moon appears in ours. Earth covers 13.5 times more visual sky area and is also about 3 times more reflective per unit area
As I mentioned in a sibling comment, the brightness of the Earth does not outweigh the lost sunlight during lunar eclipses. The near side of the Earth is darker.
I had only the vaguest notion up until 15 minutes ago of how these are being categorized, this one is described as either a brown dwarf or giant planet? https://en.wikipedia.org/wiki/CoRoT-3b
The definition isn't fuzzy, we define a brown dwarf as an object that has undergone deuterium fusion.
The fuzziness is in the physical properties needed to achieve that. 13 Jupiter masses is generally the threshold where deuterium fusion starts, but that can vary: a brown dwarf composed of only primordial H and He would need a bit more, while one with some heavier elements from previous generations of stars will be denser and need slightly less. Rotation speed also matters: a faster rotator will experience centrifugal force and thus have less interior pressure.
And there is fuzziness in what we can observe, so sometimes we're not sure if an object is a brown dwarf. We may not know its exact mass and composition, and we might not be able to tell if it's radiating energy from deuterium fusion, or just from gravitational compression, or (in a binary system) if it's just reflecting light from its companion star.
I really wanna call it a planet. It doesn't orbit a proper star, but if we call similar objects that don't orbit a star at all rogue planets I don't see why not call it just a planet.
Outside of the small probability that this may assist us in the future, has looking beyond our moon ever benefitted or even affected humanity in any way?
1. Answering where humans come from is probably one of the the oldest question we have had. All religions try to answer this in one way or the other. I say, trying to come up with scientific answers is extremely valuable.
2. We feel awe at the wonders of nature, not much different from the awe that we feel when we see great human art. Tax dollars as well as charity are used to subsidize art often. This is similar, though there is more money involved here.
3. The problems one sees in different domains are always different. Funding agencies give money to the "directly economically useless domains" because the workforce that is trained and technology that is developed can then be applied to the "directly economically useful domains". The support money to the former is much smaller than the support money to the latter, but just enough to inject fresh ideas and creativity to the latter.
Digital cameras for humanity as a whole, and satellite based telescopes for maintaining US dominance for the last 50 years and the long peace. Knowledge is power.
Before the late 70s satellites used film that was dropped back from orbit to the ground and developed to identify Cold War troop movements.
Monitoring "space weather" (paying attention to the sun/solar flares/CMEs etc) is important to keeping our earth orbiting satellites functioning. (That's without getting into what a modern "carrington event" would look like.)
No, but let's keep pouring billions into confirming that the laws of physics apply outside of our solar system - smaller objects orbiting larger ones? Who could have guessed?
I'm sympathetic to space colonization, which seems like the most optimistic long term future for humanity, but the focus on exoplanets, -moons, even signs of exo-civilizations feels like making up theories about the bottom of the ocean centuries before the invention of submarines.
this would actually be a planet, based on my understanding of celestial bodies?
moons are natural satellites orbiting planets. this "moon" is orbiting a brown dwarf.
>According to the IAU working definition (from August 2018) an exoplanet can orbit a brown dwarf. It requires a mass below 13 MJ and a mass ratio of M/Mcentral<2/(25+√{621}), or roughly 1/25. This means that an object with a mass up to 3.2 MJ around a brown dwarf with a mass of 80 MJ is considered a planet. It also means that an object with a mass up to 0.52 MJ around a brown dwarf with a mass of 13 MJ is considered a planet
Worth noting that the artist's impression is... not accurate. Both CD-35 2722 b (the brown dwarf orbiting the primary star) and CD-35 2722 b I (the exomoon orbiting the secondary) should be much closer in size. It is estimated that Jupiter is essentially the largest any gas giant can get; adding more mass will simply increase density and interior temperature until deuterium and lithium fusion and brown dwarfdom, and then at around 80 Jupiter masses, protium fusion and stardom.
Look at Barnard's Star[1], which is actually a fusing red dwarf star: it is not much bigger than Jupiter.
[1]: https://en.wikipedia.org/wiki/Barnard%27s_Star
One thing this implies is that the escape velocity of such objects increases linearly with mass, so the surface temperature they can sustain without losing mass increases quadratically with their mass. Massive super-jovian planets can orbit close to their star, limited only by tidal disruption. Some could even orbit within the outer envelope of the star for quite some time.
Ugh I got that wrong. Escape energy increases linearly with mass, so the temperature goes up linearly as well.
NASA exoplanet catalog has a neat system/star view
* https://science.nasa.gov/exoplanet-catalog/cd-35-2722-b/
It’s a perspective rendering, not orthographic. I don’t think you can reliably judge relative volume based on this image.
Nice charts in this paper that support this thesis
https://pmc.ncbi.nlm.nih.gov/articles/PMC6525489/
I kind of assumed the artist’s impression was working with perspective? The images shown in the sidebar seem to picture them at different relative sizes.
they are close in size
it's just that one is farther away from the camera
If a brown dwarf is right on the edge of stardom would it start protium fusion in only the part of itself that is the right pressure and then slowly burn out or would that ignition precipitate a pressure wave through the entire body forcing fusion to begin everywhere?
The other reply gave good info, but didn't quite answer this. Once an object's core acquires enough temperature/pressure/density to start protium fusion, it will continue, not burn out. The fusion itself increases the temperature, and the produced helium is denser than hydrogen, so the core compresses more under gravity thus increasing the pressure too. So protium fusion creates its own conditions to continue, so there's no such thing as borderline stardom; once protium fusion starts at all, it will continue and it's now a red dwarf. Fusion doesn't begin or occur everywhere, it's still only at the core, but convection will eventually (10^12 year timescale) cause all the hydrogen to have moved through the fusing region.
Thanks; this is much more concise than I could manage.
I think the key idea is fixed minimum/maximum boundaries for a lot of astrophysical phenomena—stellar protium fusion, the Chandrasekhar limit, Tolman–Oppenheimer–Volkoff limit, etc.
I appreciated both yours and the parent's comment. I read the shorter answer first, which was accessible enough to a layman like me that I was left wanting more, which made reading your comment immediately after all the more satisfying.
It should have been obvious to me (fusion duh!) that the result of the fusion is a higher density material that then increases the conditions for the reaction to take place. Both comments were immensely helpful and interesting! Thank you.
There's really a lot to unpack here. (I rewrote this response thrice...) To spoil the answers straight away, and perhaps to address some misconceptions upfront:
> If a brown dwarf is right on the edge of stardom would it start protium fusion in only the part of itself that is the right pressure
The nuclear cross-section of protium fusion in astronomical bodies is determined by temperature, pressure, and density. These variables are in turn dictated by the total mass of the object in question. Brown dwarfs never have sufficient mass for protium fusion, so they never undergo any protium fusion whatsoever. This is a hard-and-fast boundary for stardom.
> or would that ignition precipitate a pressure wave through the entire body forcing fusion to begin everywhere
The three variables above are not uniformly distributed throughout the body; there is a maximum at the centre, and fusion only happens here. Even in the Sun, about 99% of the fusion happens within about a quarter of the radius from the centre. The temperature drops rapidly thereafter, reducing the nuclear cross-section of the proton-proton chain to essentially zero. At the photosphere (surface), the temperature is ~5777 K, which is a decidedly Earthly temperature (lightning bolts are ~ 30000 K). So no, fusion does not happen everywhere.
Now, we need to discuss star formation and why brown dwarfs have never experienced protium fusion at any time in their lives. Star formation is still a very active area of research, debate, and fitting models to empirical study, and this is especially true for the detailed interior and structure of protostars and pre-main-sequence stars; hence, this is going to be quite surface-level (pun not intended).
Collapsing molecular clouds form stars. The total mass of a given cloud (or a particular region of it) sets an upper bound on the resultant object, because the total mass dictates the gravitational potential energy and hence the terminal velocity of the matter, and hence the rate of matter infall at the centre before the cloud dissipates. If the mass is low enough, the central object will become a brown dwarf, or even a large gas giant and a 'rogue planet'.
As the gas cloud collapses, the central region increases in density, temperature, and pressure, but no fusion occurs yet. Conservation of angular momentum forms a circumstellar disc, and material continues to fall onto the central region. As long as this infall continues, the central region is called a protostar. At some point the mass of protostar crosses the boundary needed for deuterium fusion; if the infall stops here, the result is a brown dwarf. If this infall continues, the mass increases beyond the boundary (~80 Jupiter masses) needed for protium fusion, and protium fusion can begin. When the infall stops and the circumstellar disc largely dissipates, the result is a pre-main-sequence star.
Note that both these very young pre-stellar objects are not yet at hydrostatic equilibrium, and are still comparatively rarefied (or 'puffy') compared to main-sequence stars; they are still collapsing, and the temperature, density, and pressure at their cores continues to increase. Only when this equilibrium is achieved and gravitational collapse is halted do stars begin life on the main sequence.
Now, it should be evident why brown dwarfs never experience protium fusion: at no point in their lives have they ever had any region in their interior hot, dense, or hyperbaric enough to have a high enough nuclear cross-section for protium fusion. At their formations, they were simply not massive enough; they continue to collapse, which admittedly provides a considerable power output—surface temperatures are ~1000 K. The largest brown dwarfs experience deuterium/tritium/lithium fusion into helium, but this also stops over time.
(Side note: in my opinion the word 'brown dwarf' is a bit of a misnomer, because look at how bright molten iron (~ 1500 K) is even in broad daylight[1]; now imagine an object ten to twenty times the radius of Earth, emitting this much heat from every square millimetre. If you approached a 'new' brown dwarf it would cast a lot of light.)
[1]: https://commons.wikimedia.org/wiki/File:Scunthorpe_Molten_St...
> It is estimated that Jupiter is essentially the largest any gas giant can get
That does not appear to be the case if we mean mass, not diameter.
https://en.wikipedia.org/wiki/Super-Jupiter
https://en.wikipedia.org/wiki/CoRoT-3b
Yes; I was under the impression that from context it was clear what I was talking about. In astrophysics, to avoid precisely this confusion, the convention is to use the adjective 'massive' when comparing, well, masses, and 'largest'/'smallest' for the dimension of length and its higher powers (radius/diameter/area/volume). For instance:
> the Sun is 3.33e5 as massive as Earth.
But... he literally said in the following sentence that adding more mass does not change size, implying that he is talking about diameter, not mass.
Correct, but the link for "super jupiter" also goes to something that astronomers are fairly sure is 1.38x the diameter of Jupiter. Much less massive of course. Meaning Jupiter's diameter is not an absolute hard limit nothing can be larger than.
https://en.wikipedia.org/wiki/HAT-P-1b
It also orbits its star in only under 5 days, so a few theoretical visualization/renderings of it would probably be quite spectacular.
Nobody said it was, he said it was "pretty much". Y'all can't read anymore.
I mean, 40% is nearly 2x the projected area, anyway
Who uses the word size to mean mass? The typical colloquial analogue to mass is "weight" - which nobody would ever conflate with "size".
A small dense planet, which orbits a star, is orbited by a larger gaseous moon. It's interesting the discovery is in Chile which has some of the best night skies, a Class 1 on the Bortle scale specifically in the Atacama Desert. Hoping to make it out there one day.
I recommend it. I'd been living in places that were a class 9 on the bortle scale, with occasional camping trips to places that were a class 5. I recently moved to the south island of New Zealand, and it's a class 4 in town and a class 1 on camping trips nearby. Completely different skies. It's rainy here though, so we don't get cloudless skies nearly as often as Chile does.
At some point I did some research and the Atacama was suggested to me as the best vantage point on earth for simple skygazing. Definitely on my bucket list.
Simple stargazing seems to be selling it short. It's the best seeing on the planet. I can do simple skygazing from my backyard. With a four hour drive I can get to a spot for pretty advanced skygazing. The ESO is building the largest telescope man has ever created in a spot you describe as good for "simple skygazing".
The skies are so dark and clear that some of the indigenous people had "constellations" made up of the dark patches in the sky instead of connecting stars.
I guess it is more of a derivative of the question: "in which bucket should we put the brown dwarf? Is it a star or a planet?". The answer is neither of course; but since it is more closely related to stars than to planets, I'm more inclined to call this satellite an exoplanet (instead of exomoon).
That being said it is still a nice finding, way more difficult to discover than "normal" exopanets.
I thought we’re supposed to call them dwarf planets now. Dwarf star, dwarf planet.
It's a problem of useful/meaningful labeling.
'Planet' comes from the Greek word for 'wanderer' which was very useful for labeling the handful of bright stars that moved through the heavens in a pattern. Then we got to the Space Age and kept calling them (and similar new additions) 'planets' even as we learned far more about them. And immediately there's a problem. Setting aside Pluto (and the Sun), you've still got Mercury on one end (5% of Earth's mass, and smaller than several moons) and Jupiter on the other end (320% of Earth's mass - more than everything else in the solar system put together, and over 1000 times Earth's volume). "Planet" stops being a word you can use with any sort of detail. (Thus the IAU definition battle and Pluto's "demotion".) Astronomers have pretty good terminology for stars, but once you go sub-stellar, the labeling rapidly gets difficult, and for good reason.
> and Jupiter on the other end (320% of Earth's mass
not %
just 320 Earth masses
> Astronomers have pretty good terminology for stars,
...do they though?
The "proper" terminology says all main sequence stars are dwarves, but nobody calls them all that in practice. Some astronomers insist on saying "yellow dwarf", but some don't really bother. In general having the only two kinds of star be "giant" or "dwarf" is contentious, but it's also contentious that there isn't a name for whatever is in the "middle". "Main-sequence star" is a broader category and doesn't apply. They're all "stars", obviously, so that isn't specific enough.
The only decent terminology is for the spectral classes, but those only work as long as you look at spectra. The moment you try to figure out what the theory says those stars would look like as proper 3D objects, things get very messy. You also immediately get the issue that star size and brightness goes O>B>A>F>G>K>M. So... it's alphabetic except it isn't. And C is something completely different and doesn't fit the brightness classification at all.
Even within stars the layman labels are a bit iffy; it is better to use the stellar classification. 'Dwarf' is badly overused, as is 'giant'.
Small-statured-person planets.
Anybody know why the brown dwarf isn't considered a planet?
Because a brown dwarf is a star? https://en.wikipedia.org/wiki/Brown_dwarf
Where is the rule that says a star can't also be a planet?
Planet++
I know this is besides the article and all, but why would the Chilean flag be the only one to have 8px left margin? This is killing me...
I believe such organisations tend to do such things very intentionally :-)
About ESO [1]
> We are an intergovernmental organisation established in 1962 supported by 16 Member States (Austria, Belgium, Czechia, Denmark, Finland, France, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), our host country Chile and strategic partners.
So Chile has a distinct status, hence the margin...?
[1]: https://www.eso.org/public/about-eso/
Obviously, how else would you do it rather than the standard left-margin notation for the host country :)
Exactly. Chile has a special status as host country of the observatory!
More than a special status as a host country, as far as I understand it is explicitly not a member state, hence it's separated from the rest of the flags (Which is curious because despite being the host country, it doesn't guarantee you being a member state of ESO).
Granted, makes sense...
The flags have also all (except for Finland, which appears slightly wider?) been squeezed into a uniform 3:2 aspect ratio; some of them (e.g. Belgium, Switzerland, United Kingdom) properly ought to have different proportions. I understand they can look more aesthetically pleasing when they’re all the same size, but it’s another little detail to notice. :-)
Now I can't unsee it :/
An important phrase from the article to consider before commenting: "This system is somewhat hard to define using Solar-System-based words like ‘planet’ and ‘moon’"
We don't really have that nomenclature. We just recently decided what a planet it for the solar system, and even that is contentious.
Redefined. We can point to at least 4 distinct definitions and lists of “planets” throughout history.
Brown dwarfs fascinate me, they can be at room temperature (range from about 2,800 K down to 250 K (roughly 2,500 °C to -23 °C / 4,500 °F to -10 °F)
You could basically have a bath in a brown dwarf, sure you might not last long, but still...
The idea of a black dwarf is also pretty wild. The universe isn't old enough for any black dwarves to exist yet, but eventually the brown ones will radiate enough heat away that they're no longer held up by the vibrational energy of the atoms they contain. They'll stop being fluffy and settle into a mode where they're held up only by electron degeneracy pressure (a.k.a the Pauli exclusion principle)... it's a bit like how neutron stars are stable because they're not so massive that they collapse to a black hole. Black dwarves will be stable because they're not so massive that they collapse to a neutron star.
What will this substance look like? Will it ring like a bell if struck? What color will it be? Will it conduct electricity? If so, how? Are the atomic nuclei now the charge carriers because the electrons are stuck? It would likely be a super-thermal-conductor, does that have any analogous properties to a super-electrical-conductor? Which of these can we observe without the sensor collapsing to degenerate matter itself?
I hope there's life around to conduct these experiments when they become possible.
Neutron stars are held up by neutron degeneracy pressure, btw, not electron degeneracy pressure. White dwarfs stars are held up by that (even though they can be very hot; the temperature needed to "lift" degeneracy increases with the mass of the object.) Even the cores of some very large stars are electron degenerate; this is why they remain stable against the "pair production instability": there aren't any states into which newly created electrons can go, suppressing pair production.
Literally not a moon, that headline is ridiculous (not posters fault)
but Nancy Grace Roman Space Telescope WILL find Earth-sized exoplanets and even REAL moons
I am stupid-excited to see it launched/first-light in my remaining lifetime (Musk better not screw it up)
For perspective on the technology, JWST "only" has 28mbps downlink
NGR has 500mbps downlink, that's right 1.5 TERABYTES PER DAY download speed
all from ONE MILLION MILES AWAY in L2 (11 seconds ping time!)
Technology is getting amazing!
I wonder if this thing in turn has something in orbit around it? At the size I wouldn't surprise me if it had satellites of its own in orbit, leaving open the question of what to call them. (I'm no astrophysicist, is this really possible I don't know, but it wouldn't surprise me. What would surprise me is if we could detect them)
https://en.wikipedia.org/wiki/Subsatellite:
“A subsatellite, also known as a submoon, moonlet or informally a moonmoon, is a "moon of a moon" or a hypothetical natural satellite that orbits the moon of a planet”
It might be helpful to describe gravitational relationships with human generational terms of parent-child, grandparent-grandchild, sibling, cousin, etc. So the Sun is the Moon's gravitational grandparent and Jupyter is its parent-sibling (Aunt/Uncle, maybe pibling upwards and nibling downwards).
I had to look it up and it is theoretically possible, they could be called sub moons or moonmoon. I'm partial to the name moonmoon personally.
David Kipling has a very good short video about this announcement: https://youtu.be/qreL7htXp98?si=vBmxwW87igExZz8l
(tl;dw it's an exciting discovery but moon is the wrong terminology for what was found)
About time!, I cant wait till we start putting large hardware on the dark side of the moon. That will make JST look like a toy.
The far side of the moon is no more or less dark than the side we see.
It is from the Moon's perspective. On the visual spectrum the Earth is much larger and more reflective than the Moon. You're looking at something like 40x greater illumination during a 'full Earth' than you get during a full Moon on Earth. Earth is also extremely noisy in the radio spectrum for radio telescopes, while the Moon itself blocks most of all of that out on the far side.
It's not. The nearside is also darker.
Earthshine is brighter than moonshine, sure. Earthshine at its brightest, delivers about 0.15W/sq meter to the moon. Sunshine meanwhile delivers 1360W/sq meter to the moon. The near side of the moon is the only side which experiences eclipses. The amount of energy from the sun is SO large, compared to earthshine, that ~1.5 eclipses per year for a few hours each represents a loss of light that outweighs the additional light gained from earthshine by about 5x.
We're talking fractions of a percent here of course, but it's not ambiguous. The near side of the moon is also the darker side.
You're right that it's noisier in radio.
Details for why ~40x: The Earth is 3.67 times larger in diameter in the lunar sky than the Moon appears in ours. Earth covers 13.5 times more visual sky area and is also about 3 times more reflective per unit area
As I mentioned in a sibling comment, the brightness of the Earth does not outweigh the lost sunlight during lunar eclipses. The near side of the Earth is darker.
The radio silence which makes the far side so attractive will also present our most significant challenge in communicating with that hardware.
> Instead, it circles a brown dwarf, an object larger than a planet, that orbits the CD-35 2722 star.
Isn't the dividing line between the largest possible gas giants and the smallest brown dwarfs a bit fuzzy?
https://en.wikipedia.org/wiki/Substellar_object
The definition of a brown dwarf is that there is enough heat and compression for deuterium and/or lithium fusion, but not protium fusion.
The exact model limit is unclear, but the physics modelling is relatively straightforward.
I had only the vaguest notion up until 15 minutes ago of how these are being categorized, this one is described as either a brown dwarf or giant planet? https://en.wikipedia.org/wiki/CoRoT-3b
see the Classification header of the page
The definition isn't fuzzy, we define a brown dwarf as an object that has undergone deuterium fusion.
The fuzziness is in the physical properties needed to achieve that. 13 Jupiter masses is generally the threshold where deuterium fusion starts, but that can vary: a brown dwarf composed of only primordial H and He would need a bit more, while one with some heavier elements from previous generations of stars will be denser and need slightly less. Rotation speed also matters: a faster rotator will experience centrifugal force and thus have less interior pressure.
And there is fuzziness in what we can observe, so sometimes we're not sure if an object is a brown dwarf. We may not know its exact mass and composition, and we might not be able to tell if it's radiating energy from deuterium fusion, or just from gravitational compression, or (in a binary system) if it's just reflecting light from its companion star.
Cool worlds says no?
https://youtube.com/shorts/qreL7htXp98?is=G9zJVbpMT0yZsLQ-
I really wanna call it a planet. It doesn't orbit a proper star, but if we call similar objects that don't orbit a star at all rogue planets I don't see why not call it just a planet.
Outside of the small probability that this may assist us in the future, has looking beyond our moon ever benefitted or even affected humanity in any way?
There are three clear benefits.
1. Answering where humans come from is probably one of the the oldest question we have had. All religions try to answer this in one way or the other. I say, trying to come up with scientific answers is extremely valuable.
2. We feel awe at the wonders of nature, not much different from the awe that we feel when we see great human art. Tax dollars as well as charity are used to subsidize art often. This is similar, though there is more money involved here.
3. The problems one sees in different domains are always different. Funding agencies give money to the "directly economically useless domains" because the workforce that is trained and technology that is developed can then be applied to the "directly economically useful domains". The support money to the former is much smaller than the support money to the latter, but just enough to inject fresh ideas and creativity to the latter.
Digital cameras for humanity as a whole, and satellite based telescopes for maintaining US dominance for the last 50 years and the long peace. Knowledge is power.
Before the late 70s satellites used film that was dropped back from orbit to the ground and developed to identify Cold War troop movements.
Monitoring "space weather" (paying attention to the sun/solar flares/CMEs etc) is important to keeping our earth orbiting satellites functioning. (That's without getting into what a modern "carrington event" would look like.)
No, but let's keep pouring billions into confirming that the laws of physics apply outside of our solar system - smaller objects orbiting larger ones? Who could have guessed?
I'm sympathetic to space colonization, which seems like the most optimistic long term future for humanity, but the focus on exoplanets, -moons, even signs of exo-civilizations feels like making up theories about the bottom of the ocean centuries before the invention of submarines.
Nice result, but I find they are selling it a bit too much. I'd rather call it an exoplanet (orbiting a brown dwarf orbiting a star).
this would actually be a planet, based on my understanding of celestial bodies? moons are natural satellites orbiting planets. this "moon" is orbiting a brown dwarf.
>According to the IAU working definition (from August 2018) an exoplanet can orbit a brown dwarf. It requires a mass below 13 MJ and a mass ratio of M/Mcentral<2/(25+√{621}), or roughly 1/25. This means that an object with a mass up to 3.2 MJ around a brown dwarf with a mass of 80 MJ is considered a planet. It also means that an object with a mass up to 0.52 MJ around a brown dwarf with a mass of 13 MJ is considered a planet
First paragraph:
> The star is being orbited by a brown dwarf, an object too massive to be a planet but too small to be a star.
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I nominate Moon 2: Electric Boogaloo.
nice work
lol
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